This invention relates to an apparatus and method for cleaning a pipeline, and more particularly to such a method and apparatus for cleaning the outside of the pipeline including a self propelled carriage moving along the pipeline.
Heretofore, apparatus has been provided including a self propelled carriage or vehicle, such as shown in U.S. Pat. No. 4,603,516 for cleaning the outside of pipe or pipeline as the self propelled carriage moves along a pipeline while supported thereon. Cleaning the outside of pipe removes loose rust, scale and dirt, to prepare the pipe for the subsequent application of a coating material on the outer surface of the pipe to minimize corrosion and prolong the service life of the pipe. In some instances, the pipe may be wrapped with an outer lining material containing an inner coating material for contacting the outer cleaned surface of the pipe. Normally abrasive particles, such as hard shot particles or grit, have been thrown by centrifugal force from an impeller wheel or the like against the outside of the pipe for cleaning the pipe. Particularly where hard shot particles of a uniform size were used previously, a relatively smooth clean outer surface of pipe was provided. The terms "pipe" and "pipeline" are interpreted herein as being the same.
It is desirable to have a roughness on the outer surface of the pipe to provide a strong bond between the pipe and coating. The roughness increases the surface area of the pipe in contact with the coating for "anchoring" the coating on the pipe. Such an increased area bond is particularly needed upon an expansion of the pipe resulting from pressure or temperature increases to maintain the bonding contact between the pipe and coating. The greater the roughness, the stronger the bond between the pipe and coating particularly for shearing stresses. An enclosed blast chamber or housing on a self propelled carriage travelling along the pipe has been utilized previously but such carriages have been relatively complex for carrying blast wheels or impellers and for assembly on and disassembly off the pipe.
Oftentimes, high pressure water is utilized for the cleaning of pipe. For example, as shown in U.S. Pat. No. 5,092,357 dated Mar. 3, 1992, a self propelled apparatus travels along a pipeline and discharges high pressure water from rotating water jets or nozzles for cleaning the outer surface of the pipeline. As shown in U.S. Pat. No. 4,552,594, a self propelled vehicle discharges high pressure water from nozzles mounted on a frame which oscillates as the apparatus moves along the pipeline for cleaning the outer surface of the pipeline.
An enclosed chamber or housing is normally provided on a travelling carriage of the pipe cleaning apparatus for maintaining the high pressure water or other cleaning material in an enclosed volume about the pipe. However, the carriages heretofore for supporting the housing and discharge nozzles for assembly on and disassembly off the pipe have been relatively complex. It is noted that in some instances a non-uniform cleaning of the pipe has been obtained as the distance of the nozzles to the outer periphery of the pipe varies substantially throughout the movement or stroke of the nozzle resulting in the water jets striking the outer periphery of the pipe at different velocities at different portions of the stroke. Thus, a non-uniform cleaning action may be obtained.